Add documentation on which mne backend to use?

[adam2392]

Inside mne.viz.backends.renderer, one can set different viz backends. The compatability table for the plotting of sensors connectivity had this before:

.. table::
       :widths: auto

       +--------------------------------------+-----------+----------+
       | **3D function:**                     | pyvistaqt | notebook |
       +======================================+===========+==========+
       | :func:`plot_vector_source_estimates` | ✓         | ✓        |
       +--------------------------------------+-----------+----------+
       | :func:`plot_source_estimates`        | ✓         | ✓        |
       +--------------------------------------+-----------+----------+
       | :func:`plot_alignment`               | ✓         | ✓        |
       +--------------------------------------+-----------+----------+
       | :func:`plot_sparse_source_estimates` | ✓         | ✓        |
       +--------------------------------------+-----------+----------+
       | :func:`plot_evoked_field`            | ✓         | ✓        |
       +--------------------------------------+-----------+----------+
       | :func:`snapshot_brain_montage`       | ✓         | ✓        |
       +--------------------------------------+-----------+----------+
       | :func:`link_brains`                  | ✓         |          |
       +--------------------------------------+-----------+----------+
       | :func:`plot_sensors_connectivity`    | ✓         | ✓        |

which we should replicate for different viz functions here?

[larsoner]

If there are no differences then I wouldn't bother. The one entry you removed in https://github.com/mne-tools/mne-python/commit/d4c5ae27c69042ea132a30d7c3fae96ae5de7cbf had checkboxes in both